1. Field of the Invention
This invention relates to a data processing system and more particularly to a microprogram-controlled system.
2. Description of the Prior Art
In the digital computer and related fields, the use of microprogramming techniques to sequentially control the operation of logic gates in a digital computer system in accordance with a microprogram, is well known as an effective means which simplifies the control system and increase its flexibility and efficiency.
There are generally two different kinds of microprogramming techniques.
The first one is called a horizontal type microprogramming which is applied to a microprogram-controlled system in which each instruction word is relatively long and, thus, each bit of the word corresponds to the operation of the gates to be controlled in accordance with the microinstruction.
Another one is called a vertical type microprogramming technique which is applied to a microprogram-controlled system in which each instruction word is short and, thus, bit information is decoded in the computer.
In the former system, the microprogramming is extremely complicated because each instruction word is long and, in addition, it must be carried out by those who do not have sufficient knowledge of the hardware. On the other hand, the latter system needs the specified hardware to decode the many bit information although the microprogramming is comparatively easy to carry out. Therefore, the functions of the microinstructions are necessarily limited to simplified ones, and quite a number of microprogramming steps are necessary in the vertical type microprogram controlled system.